This invention relates to a process for the gasification of pulverized or fine-grain solid fuels which are introduced under pressure into a gasification reactor by means of a gaseous agent. More particularly, the present invention relates to such a process wherein the gaseous agent is supplied by using a portion of the gas produced by the gasification reactor.
It is not preferred or economically feasible to process coal in a solid form to reduce the sulfur content before a gasification process. At the present time, effort is being directed to gasifying the coal in a finely-divided form and then reducing the sulfur component of the gas because it is easier to liberate the sulfur content from a gas than from a solid coal. Environmental protection is a continuously important consideration in a coal gasification process.
It is known in the art to convey solid fuel by mixing the fuel with a noncombustible gas, for example, carbon dioxide, water vapor, or some other gas usable as a gasification agent, e.g., air, oxygen or oxygen-enriched air. In many cases, the use of such gaseous substances to convey solid fuel causes difficulties in the required gasification process. For example, noncombustible gases may be totally unusable or usable in limited quantities because their introduction with the fuel inhibits the required quality of gas produced in the gasification reactor. Depending upon the type of gasification operation, there is also a fixed limit to the volume of gas per unit of weight of solid fuel that can be used as the gasification agent. In many cases, the quantity of the gasification agent usable for pneumatic conveying is insufficient for the purpose of introducing solid fuel into a gasification reactor. If oxygen-containing gases are used as the vehicle for introducing solid fuel into a gasification reactor, there is a danger of explosion before the mixture is introduced, particularly if such gases are raised to an elevated pressure. On the other hand, the reliability of ignition of the fine-grain fuel in the gasification reactor is especially important because the gasification of coal is done at high temperatures, e.g., between 1500.degree. and 2200.degree. C.